Cyber Resilience

CVE-2026-4602

Kjur Jsrsasign ≤ 11.1.1

Public PoC
Published
23 March 2026
Modified
12 August 2026
Patch / advisory
View advisory
CVSS Score v4 7.7
Click a component to see what it means
Raw vectorCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:P/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
EPSS Score 0.0049 40th percentile
Risk Priority 43 floored blend · peak EPSS

Summary

CVE-2026-4602 is a high-severity Incorrect Conversion between Numeric Types (CWE-681) vulnerability in Kjur Jsrsasign. Its CVSS base score is 7.7 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Privilege Escalation (T1068); ranked at the 40th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.

The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and SA-8 (Security and Privacy Engineering Principles) — see the control section below for these in your framework.

Deeper analysis AI-assisted summary

Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.

CVE-2026-4602 affects versions of the jsrsasign JavaScript package prior to 11.1.1, specifically due to an Incorrect Conversion between Numeric Types (CWE-681) in the ext/jsbn2.js component. The flaw arises from improper handling of negative exponents in the modPow function, which leads to the computation of incorrect modular inverses. This vulnerability has a CVSS v3.1 base score of 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H), indicating high severity primarily due to its potential for denial-of-service impacts.

An unauthenticated remote attacker can exploit this vulnerability by supplying a negative exponent to the modPow function in an application using the affected jsrsasign library. Successful exploitation forces incorrect modular inverse calculations, enabling the attacker to break RSA signature verification processes. While this disrupts cryptographic operations, the primary impact is high availability disruption, such as application crashes or hangs, without direct confidentiality or integrity violations.

Mitigation involves upgrading to jsrsasign version 11.1.1 or later, where the issue is addressed via a commit (5ea1c32bb2aa894b4bd29849839afe4f98728195) and pull request (#650) that fix negative exponent handling in jsbn2.js. Security advisories from Snyk (SNYK-JS-JSRSASIGN-15371175) and related GitHub resources confirm the patch and recommend immediate updates for applications relying on this library for cryptographic operations.

EU & UK References

Vulnerability Data

Versions of the package jsrsasign before 11.1.1 are vulnerable to Incorrect Conversion between Numeric Types due to handling negative exponents in ext/jsbn2.js. An attacker can force the computation of incorrect modular inverses and break signature verification by calling modPow with…

more

a negative exponent.

CWE(s)
CWE-681

Related Threats

MITRE ATT&CK Enterprise Techniques

T1068 Exploitation for Privilege Escalation Privilege Escalation
Adversaries may exploit software vulnerabilities in an attempt to elevate privileges.
attack.mitre.org →
T1190 Exploit Public-Facing Application Initial Access
Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.
attack.mitre.org →
T1203 Exploitation for Client Execution Execution
Adversaries may exploit software vulnerabilities in client applications to execute code.
attack.mitre.org →
T1210 Exploitation of Remote Services Lateral Movement
Adversaries may exploit remote services to gain unauthorized access to internal systems once inside of a network.
attack.mitre.org →
T1212 Exploitation for Credential Access Credential Access
Adversaries may exploit software vulnerabilities in an attempt to collect credentials.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2026-4598Same product: Kjur Jsrsasign
CVE-2026-4599Same product: Kjur Jsrsasign
CVE-2024-21484Same product: Kjur Jsrsasign
CVE-2026-4600Same product: Kjur Jsrsasign
CVE-2026-4601Same product: Kjur Jsrsasign
CVE-2023-20006Shared CWE-681
CVE-2024-7747Shared CWE-681
CVE-2026-24174Shared CWE-681
CVE-2024-1552Shared CWE-681
CVE-2026-4931Shared CWE-681

Affected Assets

kjur
jsrsasign
≤ 11.1.1

Mitigating Controls

Mitigating Controls (NIST 800-53 r5) AI

SA-11 Developer Testing and Evaluation good match

Developer testing and evaluation can discover incorrect numeric conversions through targeted test cases.

SA-8 Security and Privacy Engineering Principles partial match

Engineering principles can mandate safe numeric handling and range checks that structurally avoid bad conversions.

SI-10 Information Input Validation partial match

Input validation directly stops malformed or out-of-range numeric values from reaching conversion logic.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.PS-06 mostly match
prevents

Secure SDLC practices directly require code reviews, static analysis, and developer training that catch and prevent numeric type-conversion errors.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.8.29 Security testing in development and acceptance mostly match
finds

Security testing can detect numeric conversion defects before release.

A.8.25 Secure development life cycle partial match
prevents

Secure development lifecycle includes type-safety and conversion checks that reduce numeric truncation risks.

A.8.26 Application security requirements partial match
prevents

Application security requirements can mandate safe numeric handling and range validation.

A.8.27 Secure system architecture and engineering principles partial match
prevents

Secure architecture principles promote strong typing and safe conversion practices.

A.8.28 Secure coding partial match
prevents

Secure coding standards directly address correct numeric type conversions and overflow checks.

References